We propose to study the cytological and cytochemical phenomena that accompany axon reaction in intrinsic and extrinsic neurons. It is our premise that, in mammals, axon reaction of intrinsic neurons is regressive from the outset and that failure of CNS fiber tract regeneration results from a somal response to axonic interruption that is atrophic in character. We will study RNA and protein cytochemistry in normal and axotomized rubral nerve cells of cat by microspectrophotometry complemented by histoautoradiography. Quantitative histologic methods will be applied also. Furthermore axoplasmic transport of labelled protein will be studied. Data for intrinsic neurons will be compared with results of similar experiments on primary motor and sensory nerve cells. BIBLIOGRAPHIC REFERENCES: Barron, K.D., Dentinger, M.P., Nelson, L. and Mincy, J.E.: Ultrastructure of axonal reaction in red nucleus of cat. J. Neuropath. Exper. Neurol. 34: 222-248, 1975. Barron, K.D.: Ultrastructural changes in dendrites of central neurons during axon reaction. In: Advances in Neurology, Vol. 12, Kreutzberg, G.W., ed., Raven Press, New York, pp. 381-399, 1975.